The present invention relates to a fuse provided with a fuse element.
A typical example of conventional fuses of this type has a tubular fuse casing with a through hole formed therethrough. A cap serving as a terminal is fitted to each axial end of the fuse casing. A fuse element adapted to melt by an overcurrent is inserted through the through hole of the fuse casing, with each end of the fuse element welded to the inside of each respective cap.
An arc discharge occurs immediately after the fuse element fuses due to an overcurrent. However, should a fuse having a structure described above be made small, reduction of the space inside the through hole of the fuse casing may cause the arc discharge to increase the internal pressure of the fuse casing excessively, resulting in damage to the fuse casing.
When the fuse is made small, the distance between the two caps is reduced. As the reduction of the distance between the caps makes an arc discharge occurring at the time of fusion of the fuse element difficult to interrupt, the energy of the arc discharge may form a hole in a cap or otherwise prevent the reliable cutting off of the over current from the circuit to be protected.
In other words, the fuse described above is not easy to be made small while improving its breaking performance.
In order to solve the above problems, an object of the present invention is to provide a fuse that can be made small while improving its breaking performance.
One embodiment of the present invention includes a tubular fuse casing, a pair of metal plates which are respectively attached to the two ends of the fuse casing and have a melting point of more than 1000xc2x0 C., a pair of terminals respectively fitted to the two ends of the fuse casing in such a manner as to cover said metal plates, and a fuse element disposed in the fuse casing with each end portion of the fuse element electrically connected to each respective terminal in such a state as to be held between each respective end of the fuse casing and the metal plate attached thereto, said fuse element being able or adapted to fuse when subjected to an overcurrent.
As the fuse element of the fuse is securely held between the two lengthwise ends of the tubular fuse casing and the pair of metal plates having a melting point of more than 1000xc2x0 C., and the terminals are fitted over the metal plates, the metal plates protect the terminals from direct exposure to an arc discharge, which occurs when the fuse element fuses due to an overcurrent. Therefore, even if the internal space of the fuse casing or the distance between the terminals is reduced as a result of the fuse casing being made small, the metal plates reliably interrupt overcurrent by absorbing the energy that sustains the arc discharge. The fuse can thus be made small while achieving an improved breaking performance.
Another embodiment of the present invention is a fuse, which includes a tubular fuse casing, a pair of metal plates having a melting point of more than 1000xc2x0 C., each metal plate having a through hole and attached to each respective end of the fuse casing, a pair of terminals respectively fitted to the two ends of the fuse casing in such a manner as to cover said metal plates, a fuse element disposed in the fuse casing in such a state that each end portion of the fuse element is passed through the through hole of each respective metal plate and electrically connected to the terminal attached thereto, said fuse element being able to fuse when subjected to an overcurrent, and notches formed at each end of the fuse casing in such a manner as to face the metal plate attached to said end.
In this embodiment, the fuse has such a structure that call for respectively attaching a pair of metal plates, each of which is provided with a through hole and has a melting point of more than 1000xc2x0 C., to the two lengthwise ends of a tubular fuse casing, fitting a pair of terminals to the lengthwise ends of the fuse casing in such a manner as to cover the metal plates respectively, passing the two ends of a fuse element through the through holes of the metal plates and electrically connecting the ends of the fuse element to said terminals respectively, and forming notches at each lengthwise end of the fuse casing in such a manner as to face the corresponding metal plate so as to increase the area of the surface of each metal plate exposed to the inner space of the fuse casing. As the metal plates are capable of reliably interrupting an overcurrent by absorbing more effectively the energy of an arc discharge occurring when the fuse element fuses due to the overcurrent, the fuse can be made small while improving its breaking performance.
A third embodiment is similar to the first described embodiment above, with the addition that each metal plate and a terminal associated therewith are formed as an integral body.
By forming each metal plate and a terminal associated therewith as an integral body so as to eliminate the necessity of producing each metal plate and terminal as a separate, individual body, the fuse has a simplified structure while having the same effects as those of a fuse according to the first embodiment.